JP4165877B2 - Optical information recording / reproducing apparatus and optical information recording / reproducing method - Google Patents

Description

  The present invention relates to an optical information recording / reproducing apparatus and an optical information recording / reproducing method, and more particularly to an optical information recording / reproducing apparatus and an optical information recording / reproducing apparatus for correcting spherical aberration caused by a substrate thickness error of an optical recording medium based on reproduction signal quality. The present invention relates to an information recording / reproducing method.

  In recent years, for the purpose of recording a high definition TV, a BD (Blu-ray Disc) device has been proposed which has a higher density and a larger capacity than before. In the BD apparatus, the oscillation wavelength of the semiconductor laser is shortened and the objective lens used has a high NA.

  In general, if there is an error in the thickness of the optical disk substrate (light transmission layer) with respect to the design value, spherical aberration is generated that is proportional to the fourth power of the objective lens NA and inversely proportional to the wavelength, and the spot quality on the optical recording medium deteriorates. However, it is known that the recording / reproducing performance is lowered. Therefore, in the case of a BD device having a short wavelength and a high NA, since spherical aberration is very likely to occur compared to a DVD device or the like, it is necessary to correct the spherical aberration, and an apparatus for correcting the spherical aberration is required. Proposed. In addition, a technique for making a plurality of data recording surfaces, for example, two layers, has been studied, and correction of spherical aberration is necessary in order to focus the light spot on two layers having different cover thicknesses without spherical aberration.

As a technique for correcting spherical aberration, for example, Patent Document 1 discloses a technique for detecting an index indicating the quality of a reproduction signal such as the amplitude and jitter of the reproduction signal and controlling the spherical aberration correction element.
Japanese Patent Laid-Open No. 2003-233917

  However, controlling the spherical aberration correction element using amplitude and jitter for evaluating the quality of the reproduced signal is not necessarily an effective method in terms of accuracy of spherical aberration correction in recent years when high-density recording is progressing, There has been a demand for an optical information recording / reproducing apparatus and an optical information recording / reproducing method such as an optical disc apparatus capable of correcting spherical aberration easily and reliably with high accuracy.

  In recent years, the PRML system has been increasingly used as a data detection system because of high-density recording and the like in optical disk devices. In the PRML system, the playback signal is equalized by the PR system according to the characteristics of the recording / playback system, and decoding processing is performed by maximum likelihood decoding such as Viterbi decoding, thereby obtaining data with a low error rate even in a playback signal with large intersymbol interference. be able to.

  In the present invention, a reproduction signal quality evaluation index using a PRML method such as a SAM (Sequenced Amplitude Margin) is used as an evaluation index of the quality of a reproduction signal instead of the amplitude and jitter disclosed in Patent Document 1 and the like. The spherical aberration correction amount is determined based on the signal quality evaluation index, and spherical aberration is generated. An optical disc apparatus using the PRML method is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-051163, and this publication uses SAM as a reproduction signal quality evaluation index using the PRML method. It is disclosed that optimization such as optimum recording power, servo offset, and equalization count of a waveform equalization circuit is performed.

  In the present invention, as described above, the spherical aberration correction amount is determined based on the reproduction signal quality evaluation index using the PRML method such as SAM to generate the spherical aberration, and the coefficient of the equalization filter is sequentially updated. By providing the equalizing means, the waveform equalization is maintained in an optimum state even when the state of the spherical aberration changes. If the coefficient of the equalization filter is not sequentially updated and the spherical aberration correction operation is performed with the predetermined coefficient, the coefficient may be corrected to an incorrect place different from the original spherical aberration best point depending on the coefficient setting. May end up. This operation will be described in detail in an embodiment of the invention described later with reference to FIG.

That is, a first invention according to the present application is an optical information recording / reproducing apparatus that records and reproduces information by condensing a light source and a light beam from the light source on an optical recording medium.
An objective lens for condensing the luminous flux;
Spherical aberration generating means for generating spherical aberration in the luminous flux between the light source and the objective lens;
A sensor that receives light from the optical recording medium and converts it into an electrical signal;
An equalization filter for equalizing the output of the sensor to a predetermined partial response characteristic;
Quality evaluation means for measuring the reproduction quality of the output signal of the equalization filter;
Adaptive equalization means for updating the coefficient of the equalization filter,
When driving the spherical aberration generating means, the reproduction quality of the output signal of the equalization filter is measured using the quality evaluation means with the coefficient of the equalization filter being sequentially updated by the adaptive equalization means. Then, the amount of aberration generated by the spherical aberration generating means is determined based on the measured reproduction quality.

  In the above configuration, the spherical aberration generating means corrects the spherical aberration due to the substrate thickness error of the medium, the sensor converts the information recorded on the medium into an electric signal, and sequentially updates the coefficients of the equalization filter and the equalization filter. The output of the sensor means is equalized to a predetermined partial response characteristic by the equalizing means. The quality evaluation means evaluates the reproduction signal quality reproduced from the medium and equalized by the equalization filter, and determines the aberration generated by the spherical aberration generation means according to the reproduction quality. By generating the optimum spherical aberration in the spherical aberration generating means, the spherical aberration on the medium surface can be brought into the best state and the best recording / reproducing performance can be exhibited. Also, the adaptive equalization operation can be performed quickly by updating the coefficient of the equalization filter based on the output of the equalization filter.

  The second invention according to the present application is characterized in that, in the first invention, the coefficient of the equalization filter is updated by the adaptive equalization means even during measurement by the quality evaluation means. To do.

  In the above configuration, the coefficient of the equalization filter is updated even during measurement by the quality evaluation unit, so that the best reproduction signal can be used in determining the aberration generated by the spherical aberration generation unit.

  Further, according to a third aspect of the present application, in the first aspect, the coefficient of the equalization filter is updated by the adaptive equalization unit before each measurement by the quality evaluation unit. It is characterized by.

  In the above configuration, the coefficient of the equalization filter is updated every time the quality evaluation unit performs measurement and before the measurement, so that the determination of the aberration generated by the spherical aberration generation unit is performed with the best reproduction signal. be able to.

Further, a fourth invention according to the present application is the above-described first invention, further comprising a maximum likelihood decoding means for binarizing the output of the equalization filter by a maximum likelihood decoding method, wherein the quality evaluation means is the maximum likelihood. Measure playback quality based on likelihood in decoding means,
The adaptive equalization means updates the coefficient of the equalization filter based on the equalization filter output.

  In the above configuration, the maximum likelihood decoding means binarizes the reproduction signal based on the maximum likelihood decoding method, and measures the reproduction quality based on the likelihood, thereby measuring the reproduction quality with higher accuracy. This makes it possible to correct spherical aberration accurately and quickly.

According to a fifth aspect of the present application, there is provided an optical information recording / reproducing method for recording and reproducing information by condensing a light source and a light beam from the light source on an optical recording medium.
Receiving light from the optical recording medium and converting it into an electrical signal;
The converted electric signals, the equalization filter whose coefficients are updated, and equalized to a predetermined partial response characteristic in a state that the coefficient of the equalizing filter is sequentially updated,
Measure the playback quality of the equalized signal,
A spherical aberration amount determined based on the reproduction quality is generated in a light beam from the light source.

  According to a sixth aspect of the present application, in the fifth aspect, the coefficient of the equalization filter is updated even during measurement of quality evaluation.

  Further, a seventh invention according to the present application is the fifth invention, wherein the equalization filter coefficient update is performed before each measurement of the quality evaluation, and the equalization is performed during the measurement of the quality evaluation. The filter coefficient is not updated.

Further, an eighth invention according to the present application is the above-mentioned fifth invention, wherein the output of the equalization filter is binarized by a maximum likelihood decoding method, and the quality evaluation is based on the likelihood in the maximum likelihood decoding. Measure
The coefficient of the equalization filter is updated based on the equalization filter output.

  According to the present invention, the spherical aberration generating means corrects the spherical aberration due to the substrate thickness error of the medium, the sensor converts the information recorded on the medium into an electric signal, and the equalizing filter and the adaptive equalizing means The output is equalized to a predetermined partial response characteristic. The quality evaluation means evaluates the reproduction signal quality reproduced from the medium and equalized by the equalization filter, and determines the aberration generated by the spherical aberration generation means according to the reproduction quality. By generating the optimum spherical aberration in the spherical aberration generating means, the spherical aberration on the medium surface can be brought into the best state and the best recording / reproducing performance can be exhibited. Also, the adaptive equalization operation can be performed quickly by updating the coefficient of the equalization filter based on the output of the equalization filter.

  Further, according to the present invention, the coefficient of the equalization filter is constantly updated during the measurement of the quality evaluation means, so that the determination of the aberration generated by the spherical aberration generating means can always be performed with the best reproduction signal. it can.

  Further, according to the present invention, the coefficient update of the equalization filter is performed every time the quality evaluation unit performs measurement and before the measurement, so that it is always the best in determining the aberration generated by the spherical aberration generation unit. This can be done with the reproduction signal.

  Further, according to the present invention, the maximum likelihood decoding means binarizes the reproduction signal based on the maximum likelihood decoding method, and measures the reproduction quality based on this likelihood, thereby improving the reproduction quality with higher accuracy. It becomes possible to measure and spherical aberration can be corrected accurately and quickly.

(First embodiment)
Hereinafter, the device according to the present invention will be described in detail with reference to the drawings.

<Optical System Configuration of Optical Pickup OPU 202>
FIG. 10 is an example of an optical pickup according to the present embodiment. The beam emitted from the semiconductor laser 1 is divided into three beams by the diffraction grating 2, converted into parallel light by the collimator 3, and enters the polarization beam splitter 4 with beam shaping. A part of the beam is reflected, enters the APC sensor 5, and is used for monitoring the amount of light emitted from the semiconductor laser 1. The transmitted beam is condensed on the recording layer surface via the light transmission layer on the optical disk 13 by the objective lens 12 through the quarter-wave plate 6, the lens 7 and the lens 8, and is used for reproducing and recording information. The The beam reflected by the optical disc 13 passes through the objective lens 12, the lens 8, the lens 7, and the ¼ wavelength plate 6, is reflected by the polarization beam splitter 4 with beam shaping, and passes through the sensor lens 14 to RF / The light enters the servo sensor 15 and is used for reproducing the information signal.

Here, the lens 7 and the lens 8 are held so that the lens 7 is fixed, and the lens 8 is held by the electromagnetic driving means 10 so that the distance between the lens 7 and the lens 7 in the optical axis direction is variable, thereby forming the spherical aberration generating means 11. ing. The shape of the lens 7 and the lens 8 and the glass material are configured such that only spherical aberration occurs when the lens interval changes. The electromagnetic driving means 10 moves the lens 8 on the micron order with a lead screw using a stepping motor, for example.
<Overall Configuration of Information Reproducing Device 200 and Series of Operations>
In FIG. 2, an information reproducing apparatus 200 includes a disk-shaped medium (hereinafter referred to as “disk”) 201, an optical pickup (OPU) 202, a spindle motor (SPM) 203, a servo DSP (Digital Signal Processor) 208, an RF preamplifier 204, An AGC (Auto Gain Control) / Filter 205, an A / D converter 206, a reproduction processor 207, a drive controller 209, a memory 211, a memory control 210, and a data bus 212 are included.

  In the information reproducing apparatus 200, the memory 211 is a memory space used by time sharing in each functional block via the data bus 212, and is controlled and managed by the memory control 210 via the drive controller 209.

  The drive controller 209 includes a central processing unit (CPU), and receives and executes a user-specified command via the data bus 212 or executes a predetermined program to control the entire system of the information reproducing apparatus 200.

  The optical pickup 202 performs laser light irradiation and information detection on the disk 201. For information detection, the amount of light reflected from the disk medium is detected and the reflected light is photoelectrically converted to obtain a reproduced electrical signal.

  The servo DSP 208 has a function of controlling the entire drive control to the disk 201, and controls the position of the optical pickup 202 on the disk 201 at a predetermined address by a traverse motor (not shown). Further, focus control and tracking control are performed by controlling an actuator in the optical pickup 202. Further, the laser 201 is controlled to be driven at a predetermined number of rotations by the laser emission light amount control in the optical pickup 202 and the spindle motor 203.

  Further, the servo DSP 208 gives spherical aberration to the light flux by driving the electromagnetic driving means 10 of the spherical aberration generating means 11 in the optical pickup 202 shown in FIG. 10 according to the command of the drive controller 209.

  Information reproduction processing from a disc will be described. The weak reproduction signal obtained from the optical pickup 202 is amplified by the RF preamplifier 204. Thereafter, the AGC / Filter 205 performs gain control and band limitation to a predetermined level. The A / D converter 206 converts the input analog signal into a digital signal. These are optimally controlled to predetermined characteristics from a drive controller 209 by a control line (not shown). Subsequently, reproduction signal processing is performed in the reproduction processor 207 and information data is transmitted to the data bus 212.

<Detailed functions and series of operations of the playback processor 207>
Next, reproduction signal processing of the reproduction processor 207 will be described in detail with reference to FIG. In FIG. 3, 301 is waveform equalization, 302 is Viterbi decoding, 303 is demodulation, 304 is ECC (Error Correct Code), 305 is SAM (Sequential Amplitude Margin) value calculation.

  The signal input to the reproduction processor 207 is subjected to a PLL (not shown) and a clock component synchronized with the reproduction signal is extracted. This clock is used for the processing timing of the reproduction processor.

  The disc information shown in the present embodiment is recorded by performing NRZI conversion on a known (1, 7) RLL code, and the minimum inversion interval is 2.

  Waveform equalization 301 performs waveform equalization having the characteristics of partial response PR (1, 2, 2, 1). PR (1, 2, 2, 1) is represented by the following formula.

ここでｙ〔ｋ〕：ＰＲ出力値、ｄ_k：現在の時刻ｋにおける記録符号、ｄ_k-1：１クロック前の時刻ｋ−１における記録符号、ｄ_k-2：２クロック前の時刻ｋ−２における記録符号、ｄ_k-3：３クロック前の時刻ｋ−３における記録符号である。

Where y [k]: PR output value, d _k : recording code at the current time k, d _k−1 : recording code at time k−1 before 1 clock, d _k−2 : time k before 2 clocks. -2 recording code, d _k-3 : recording code at time k-3 three clocks before.

  The waveform equalization 301 is an adaptive equalization filter, and a more detailed block diagram is shown in FIG.

  In FIG. 9, the waveform equalization 301 is configured by an N-tap FIR type adaptive filter, and the reproduction signal x (n) includes N−1 delay units 311 and N coefficient multipliers 312. The sum obtained by adding the output from the adder by the adder 313 is the filter output y (n).

  The adaptive operation is performed as follows.

  The reproduction signal x (n) passes through an N-tap FIR filter and is output as a filter output y (n). The output is input to the Viterbi decoder and error signal generation circuit 314. The error signal generation circuit 314 calculates the difference between the ideal waveform and the filter output y (n), applies a predetermined coefficient, and outputs the result to the coefficient update circuit 315.

  When a test pattern recorded in advance at a predetermined location on the disc is reproduced, the ideal waveform is known in advance. Therefore, the ideal waveform may be output and compared with the reproduced test pattern. In addition, when an adaptive operation is performed by reproducing a signal whose recorded pattern is unknown, such as user data, the filter output level is determined, and the determined value is set as an ideal waveform. For example, in the case of PR (1, 2, 2, 1) as in this embodiment, the ideal output value is 7 values of 0, 1, 2, 3, 4, 5, 6, and therefore the filter output level is 7 The determination can be made by simply comparing the levels with a comparator that can determine the value.

  The coefficient update circuit multiplies the output signal of the error signal generation circuit by the input signal of each coefficient multiplication circuit and adds the result to the current coefficient to obtain the next coefficient.

  As this operation continues, the coefficients are optimized, and the error approaches 0, and the adaptive operation converges.

  This waveform equalization 301 has a mode for determining whether or not to perform a coefficient update operation (adaptive operation), and makes the adaptive operation active / inactive according to a command from the drive controller. When not in operation, the output of the error signal generation circuit may be 0 regardless of the input signal.

  An adaptive equalizer is disclosed in, for example, Japanese Patent Laid-Open No. 2001-014804.

  FIG. 6 shows a state transition diagram based on (1, 7) RLL and PR (1, 2, 2, 1). Each state transitions to the next state according to the PR value. Subsequently, the decoded bit is output according to the state transition. FIG. 7 shows a trellis diagram obtained by developing the state transition diagram of FIG. 6 in the time axis direction.

In the Viterbi decoding, according to the trellis diagram shown in FIG. 7, the path metrics m ₀₀₀ [k] to m ₁₁₁ [k] at time k in each state are the metrics m ₀₀₀ [k−1] in a predetermined state at time k−1. ˜m ₁₁₁ [k−1] and the actual PR output value y [k] at time k are obtained by the following calculation formula X.

状態Ｓ（ｄ_k-2、ｄ_k-1、ｄ_k）とは、現時刻の復号データがｄ_k、１時刻前の復号データがｄ_k-1、２時刻前の復号データがｄ_k-2であることを示す。

State _{S (d k-2, d} k-1, d k) and the decoded data of the current time is d _k, 1 times before the decoded data d _k-1, 2 times the previous decoded data d _{k- 2} is shown.

  In the state S000, the state S001, the state S110, and the state S111, since two paths merge at each time, the path with the smaller path metric value is selected as the surviving path from the two paths that merge. Here, the path is a history of the state that has been passed, and is also called a state transition sequence.

  Also, as shown in the trellis diagram of FIG. 7, when transitioning from time k-1 to each state of time k, the ideal output value of PR (1, 2, 2, 1) determined by each transition and the actual The Euclidean distance from the output value obtained by PR (1, 2, 2, 1) processing of the reproduction signal is added as a branch metric. The ideal output value of PR (1, 2, 2, 1) is 7 values of 0, 1, 2, 3, 4, 5, 6.

  Next, operations of the Viterbi decoding 302 and the SAM value calculation 305 will be described. FIG. 8 shows functional blocks of the Viterbi decoding 302 and the SAM value calculation 305. In FIG. 8, 801 is a metric calculation, 802 is an addition / comparison / selection, 804 is a path memory, 805 is a metric difference calculation, 806 is a standard deviation calculation, and 807 and 808 are registers.

  Sample values output from PR (1, 2, 2, 1) are input to Viterbi decoding 302, and a metric calculation 801 calculates a branch metric. The branch metric is added / compared / selected 802 with the formula x implemented.

  Add the branch metric at time k and the path metric value of each state at time k−1, compare the addition results, and select the smaller value as the path metric value of each state at time k The new path metric value is stored in the register 807. In response to the state transition of the selected path metric value, the path memory 804 outputs the most likely data series.

  In other words, by updating the path metric value, it is possible to calculate the probability of the path (state transition sequence) from time n before. Among them, by outputting a data sequence of a state transition sequence corresponding to the minimum path metric value in a predetermined section, a data sequence corresponding to the most probable path is output as a decoding result.

  Next, the SAM value calculation 305 will be described. SAM (Sequenced Amplitude Margin) is the difference between the most probable path and the next most probable path in Viterbi decoding. For example, Tim Perkins and Zachary A. Keirn, “A Window-Margin-Like Procedure for Evaluating PRML Channel Performance”, IEEE Transaction on Magnetics, Vol. 21 No. 2, March 1995.

  In FIG. 8, the metric difference 805 stores the path metric difference between the most probable path and the next most likely path from the addition / comparison / selection 802 output result in the register 808.

  In Viterbi decoding, the most probable path, that is, the path that minimizes the accumulated error (path metric value) between the sample value of the data series and the waveform equalization ideal value at each time is selected. Therefore, the larger the difference between the most probable path and the next most probable path metric, the higher the reliability of the former, and the higher the reliability of the decoded data. Conversely, if the metric difference between the most probable path and the next most probable path is small, there is a high possibility that an error will occur in the alternative, and the reliability of the decoded data will be low.

  FIG. 4 shows a histogram of the output values of the metric difference calculation 805. In FIG. 4, the horizontal axis is the metric difference, and the vertical axis is the frequency number. Among the plurality of histograms obtained by accumulating the metric differences at the respective sample points, the histogram located in the region having the smallest metric difference is exemplified. . In FIG. 4, three types of plots in which the quality of the reproduced signal is changed are displayed. In the region where the metric difference on the horizontal axis is small, the most probable path and the next most probable path metric are close to each other, so that a Viterbi decoding is likely to cause a path identification error, that is, an error in decoded data. Therefore, in 4a, 4b, and 4c of FIG. 4, when attention is paid to the frequency of the region where the metric difference is small, since 4c> 4b> 4a, the possibility that the reproduced signal 4c is erroneously determined in Viterbi decoding is the highest. In other words, the signal quality is poor. Subsequently, the reproduced signal 4b and the reproduced signal 4a have the lowest probability of erroneous determination, that is, the signal quality is good.

  The standard deviation calculation 806 in FIG. 8 has a function of obtaining the standard deviation from the metric difference histogram shown in FIG. In the example of FIG. 4, the standard deviation is 4c> 4b> 4a, and the quality of the reproduction signal can be determined by the degree of the standard deviation.

  FIG. 5 is a diagram showing the correlation between the SAM value and the error rate (bit error rate). As shown in the figure, the SAM value obtained from Viterbi decoding shows a high correlation with the error rate.

  Subsequently, the process returns to the reproduction processor of FIG. The demodulator 303 is a demodulator that demodulates the decoded data string by (1, 7) RLL, and an information reproduction signal that has been error-corrected by the ECC 304 at the subsequent stage is output to the data bus 212.

  The operation procedure of the present embodiment will be described along the flowchart of FIG.

  When the optical disk apparatus according to the present embodiment is activated, the spindle is activated, the laser is turned on, the servo is activated, and the preparation for reading data on the medium is completed.

  When the spherical aberration correction routine starts (step S1), first, the spherical aberration generating means 11 shown in FIG. 10 is set to a predetermined start position (step S2).

  For example, when the thickness of the medium substrate is standard, the position is deviated by a predetermined amount from the reference position on the design value that gives aberration that eliminates spherical aberration on the medium surface. The amount of spherical aberration generated is −4. For example, the lens 8 is moved by 10 μm per unit. -4 is a state in which the 40 μm lens 8 is moved from the reference position in a direction approaching the lens 7.

  Next, the drive controller issues a start instruction for adaptive operation to the waveform equalization 301 (step S3).

  As a result, the waveform equalization 301 reads data recorded on the medium in advance, and starts updating the coefficients so that the output is close to the PR (1, 2, 2, 1) characteristic.

  Next, the drive controller stores the output signal of the SAM value calculation 305 in a memory or the like as an evaluation index in association with the correction amount −4 (step S4).

  Next, the drive controller confirms whether the spherical aberration spherical aberration generating means is at the end position (step S5).

  The end position is a state in which the spherical aberration generation amount is set to +4, and the 40 μm lens 8 is moved by a method of moving away from the lens 7 from the reference position.

  If it is not the end position, the spherical aberration correction amount is increased by 1 until the end position is reached (step S6), and the SAM value is measured and stored in association with the correction amount (step S4). Since the correction amount is increased by one, the lens 8 is moved by 10 μm and the reproduction signal quality at that location is evaluated.

When the correction amount is plotted on the horizontal axis and the SAM value is plotted on the vertical axis, a graph represented by a circle in FIG. 11 is drawn. In order to obtain the optimal spherical aberration correction amount, the SAM value associated with the stored correction amount is used. Two correction amounts where the SAM value crosses a reference value (for example, a SAM value corresponding to a bit error rate of 10 ⁻⁴ ) are obtained, and the median value of the two correction amounts is set as an optimal spherical aberration correction amount. In order to accurately obtain the optimum spherical aberration correction amount from the discrete correction amount, a correction amount that straddles the reference value is obtained from each correction amount by linear interpolation or the like. In the example of ○ in FIG. 11, the correction amount straddling the reference value on the minus side is 3.3 on the −3.0 plus side, so the optimal spherical aberration correction amount is found to be 0.15. The obtained correction amount is set in the spherical aberration generating means 11 (step S7).

  When the correction of the spherical aberration is completed (step S8), the optical disc apparatus is ready to record / reproduce user data.

  At the beginning of the spherical aberration correction routine, an adaptive equalization operation is started in the waveform equalization 301. During the spherical aberration correction routine, the PR (1, 2, 2, 1) characteristic is always brought close to the signal quality and the spherical surface is improved. When the aberration correction means 11 changes the aberration and evaluates the SAM value, the waveform distortion caused by the aberration is in the best state by the waveform equalization 301, so that the optimum spherical aberration can be obtained accurately.

  For example, when the spherical aberration correction operation is performed with a predetermined coefficient without performing the adaptive equalization operation on the waveform equalization 301 every time under the same conditions, depending on the setting of the coefficient, the original spherical aberration is the best point. In some cases, waveform equalization works in a bad direction, resulting in the result represented by ▽ in FIG. When the spherical aberration correction amount is obtained from the result of FIG. 11 ▽, the correction amount straddling the reference value on the minus side is 2.3 on the −2.5 plus side, so the optimum spherical aberration correction amount is −0.1. As a result, it is corrected to a wrong place different from the case of ○. According to the present embodiment, since the waveform equalization 301 is always kept in an optimum state even when the state of the spherical aberration changes, such a problem is eliminated.

  In this embodiment, the SAM value is used as the reproduction signal quality evaluation index. However, the amplitude value of a predetermined pattern (for example, 2T pattern) or the like may be used as long as it is a signal after waveform equalization.

  Further, although the optical system as shown in FIG. 10 is used as the spherical aberration correction means, any device can be used as long as it can correct the spherical aberration, such as a liquid crystal element.

(Second Embodiment)
The configuration of this embodiment is the same as that of the first embodiment, but the operation procedure in the spherical aberration correction routine is different.

  The operation procedure of the present embodiment will be described along the flowchart of FIG.

  When the optical disk apparatus according to the present embodiment is activated, the spindle is activated, the laser is turned on, the servo is activated, and the preparation for reading data on the medium is completed.

  When the spherical aberration correction routine is started (step S1), first, the spherical aberration generating means 11 is set to a predetermined start position (step S2). The meaning of the start position is the same as in the first embodiment.

  Next, the drive controller issues a start instruction for adaptive operation to the waveform equalization 301 (step S3). The operation up to this point is the same as in the first embodiment.

  As a result, the waveform equalization 301 starts reading the data recorded on the medium in advance and updates the coefficients so that the output is close to the PR (1, 2, 2, 1) characteristic.

  Next, the drive controller monitors the error signal of the error signal generation circuit in the waveform equalization 301, checks whether the error signal is within a predetermined range, and if it is within the predetermined range, the adaptive operation has converged. Judge. Confirmation is continued until it falls within the predetermined range (step S4).

  Next, the drive controller sets the output of the error signal generation circuit in the waveform equalization 301 to 0 and stops the adaptive operation (step S5). At this time, the waveform equalization 301 stops at the state of the best equalization characteristic coefficient at the spherical aberration start position.

  Next, the drive controller associates the output signal of the SAM value calculation 305 with the correction amount −4 and stores it in a memory or the like as an evaluation index (step S6).

  Next, the drive controller confirms whether the spherical aberration spherical aberration generating means is at the end position (step S7).

  The end position is a state in which the spherical aberration correction amount is +4, and the 40 μm lens 8 is moved in the direction away from the lens 7 when viewed from the reference position.

  If it is not the end position, the spherical aberration correction amount is increased by 1 until the end position is reached (step S9), the adaptive equalization operation is started (step S3), the convergence check (step S4), and the adaptive equalization operation is stopped ( Step S5), the SAM value is measured and stored in association with the correction amount (Step S6).

  The operation for determining the correction amount from the SAM value is also the same as in the first embodiment.

  Next, the obtained correction amount is set in the spherical aberration generating means 11 (step S8).

  When the correction of the spherical aberration is completed (step S10), the optical disc apparatus is ready to record / reproduce user data.

  Each time the spherical aberration correction correction means is moved, the adaptive equalization operation of the waveform equalization 301 is started, and during the spherical aberration correction routine, the PR (1, 2, 2, 1) characteristic is always approached, and the signal quality is improved. As a result, the waveform distortion due to the aberration is equalized to the best waveform, and when the SAM value is evaluated by changing the aberration by the spherical aberration correction means 11, the waveform equalization 301 is in the best state. Therefore, the optimum spherical aberration can be accurately obtained.

  In the present embodiment, since the SAM value is evaluated after waiting for the adaptive operation to converge, there is no evaluation based on the waveform during the adaptive operation.

  Further, since the adaptive operation is stopped after convergence, the adaptive operation does not malfunction due to noise, scratches on the disk, etc. when evaluating the SAM value.

  In addition, as in the first embodiment, the result shown by ▽ in FIG. 11 is obtained, and there is no problem of correcting to the wrong place.

  In this embodiment, the drive controller monitors the convergence state of the adaptive operation. However, a function (such as an interrupt function) may be prepared in the adaptive equalization circuit to detect convergence and notify the controller. Alternatively, the adaptive operation may be stopped after a fixed waiting time for the standard convergence time. In either case, the drive controller does not need to monitor the convergence state, so the load on the drive controller is reduced.

  In this embodiment, the SAM value is used as the reproduction signal quality evaluation index. However, the amplitude value of a predetermined pattern (for example, 2T pattern) or the like may be used as long as the signal is after waveform equalization.

  Further, although the optical system as shown in FIG. 1 is used as the spherical aberration correcting means, any device may be used as long as it can correct the spherical aberration, such as a liquid crystal element.

  The present invention is applied to a DVD that requires spherical aberration correction, a BD (Blu-ray Disc) device that has a higher density and a larger capacity, and the like.

It is a flowchart which shows the operation | movement of the 1st Embodiment of this invention. It is a block diagram of an information reproducing device. 3 is a block diagram of a playback processor. FIG. It is a histogram of a metric difference. It is a figure which shows the correlation of a SAM value and an error rate. It is a state transition diagram. It is a trellis diagram. It is a figure which shows the functional block of Viterbi decoding and SAM value calculation. It is a block diagram of an adaptive equalization filter. It is a figure which shows the optical system structure of the optical pick-up OPU202. It is a figure which shows the relationship between a correction amount and a SAM value. It is a flowchart which shows the operation | movement of the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 3 Collimator 4 Polarizing beam splitter 7, 8 Lens 11 Spherical aberration generating means 12 Objective lens 15 RF / servo sensor 200 Information reproducing device 201 Optical disc 202 Optical pickup 203 Spindle motor 208 Servo DSP
207 Playback processor 209 Drive controller 210 Memory control unit 211 Memory 212 Data bus 301 Waveform equalization 302 Viterbi decoding 303 ECC
303 Demodulation 305 SAM value calculation

Claims (8)

In an optical information recording / reproducing apparatus for recording and reproducing information by condensing a light source and a light beam from the light source on an optical recording medium,
An objective lens for condensing the luminous flux;
Spherical aberration generating means for generating spherical aberration in the luminous flux between the light source and the objective lens;
A sensor that receives light from the optical recording medium and converts it into an electrical signal;
An equalization filter for equalizing the output of the sensor to a predetermined partial response characteristic;
Quality evaluation means for measuring the reproduction quality of the output signal of the equalization filter;
Adaptive equalization means for updating the coefficient of the equalization filter,
When driving the spherical aberration generating means, the reproduction quality of the output signal of the equalization filter is measured using the quality evaluation means with the coefficient of the equalization filter being sequentially updated by the adaptive equalization means. and, wherein the measured on the basis of the reproduction quality, the optical information recording and reproducing apparatus characterized by determining the occurrence aberration of the spherical aberration generating means.   2. The optical information recording / reproducing apparatus according to claim 1, wherein the coefficient of the equalization filter is updated by the adaptive equalization unit even during measurement by the quality evaluation unit.   The coefficient of the equalization filter by the adaptive equalization means is updated before each measurement by the quality evaluation means, and the coefficient of the equalization filter is not updated during the measurement by the quality evaluation means. The optical information recording / reproducing apparatus according to claim 1. A maximum likelihood decoding means for binarizing the output of the equalization filter by a maximum likelihood decoding method, wherein the quality evaluation means measures the reproduction quality based on the likelihood in the maximum likelihood decoding means;
2. The optical information recording / reproducing apparatus according to claim 1, wherein the adaptive equalization unit updates a coefficient of the equalization filter based on an output of the equalization filter. In an optical information recording / reproducing method for recording and reproducing information by condensing a light source and a light beam from the light source on an optical recording medium,
Receiving light from the optical recording medium and converting it into an electrical signal;
The converted electric signals, the equalization filter whose coefficients are updated, and equalized to a predetermined partial response characteristic in a state that the coefficient of the equalizing filter is sequentially updated,
Measure the playback quality of the equalized signal,
An optical information recording / reproducing method, wherein a spherical aberration amount determined based on the reproduction quality is generated in a light beam from the light source.   6. The optical information recording / reproducing method according to claim 5, wherein the coefficient of the equalization filter is updated even during the measurement of the reproduction quality.   6. The coefficient of the equalization filter is updated before each measurement of the reproduction quality, and the coefficient of the equalization filter is not updated during the measurement of the reproduction quality. The optical information recording / reproducing method described. Binarizing the output of the equalization filter by a maximum likelihood decoding method, measuring the reproduction quality based on the likelihood in the maximum likelihood decoding,
6. The optical information recording / reproducing method according to claim 5, wherein a coefficient of the equalization filter is updated based on an output of the equalization filter.

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